(1) Field of the Invention:
The present invention relates to a temperature control indicating apparatus of a hot runner in a thermoplastic synthetic resin injection molding system.
(2) Description of the Prior Art:
Conventionally, a temperature control means of a hot runner as shown in FIG. 4 is known.
Referring to the drawing, numeral 1 designates a hot runner (or called a probe), numeral 2 designates a tip heater (SPEAR* tip heater) set on the pointed end of the hot runner, numeral 3 designates a body heater set in the said hot runner, numeral 4 designates an analog indicator of a tip current acting on the said tip heater 2. The analog indicator 4 is connected with power control circuit 5. FNT * The word "SPEAR" is the Applicant's trademark.
Numeral 6 designates an analog indicator of a body current acting on the body heater 3, and the analog indicator 6 is connected with a power control circuit 7. Numeral 8 and 9 designate current control circuits respectively connected with the power control circuits 5 and 7, numeral 10 designates a temperature control circuit of the side of the body heater 3, the temperature control circuit 10 has an analog temperature indicator 11, and connects with a temperature setting part 12 and a temperature sensor 13 set in the hot runner 1, thereby a circuit 14 based on temperature control is constituted. Numeral 15 designates a current setting part, thereby a circuit 16 based on current control is constituted to the said circuit 14. Numeral 17 designates a change-over switch of the both circuits 14 and 16.
Numeral 18 designates a preheat current setting part of the side of the tip heater 2 and numeral 19 designates a tip current setting part. These parts are respectively constituted so as to change with a switch 20. Numeral 21 designates a timer circuit which acts by inputting signals originated each time of injection molding operation, the timer circuit 21 is constituted so as to change the switch 20.
In the constitution as described above, for the body heater 3, the temperature of the hot runner 1 which is sensed with the temperature sensor 13 and the desired setting temperature which is set at the temperature setting part 12 are controlled by operation in the temperature control circuit 10. The temperature is displayed with the analog temperature indicator 11, and thermostatically maintained by allowing necessary current to flow through the next steps of the control circuit 9 and the power control circuit 7 to the body heater 3. Further, in this case, the switch 20 is changed to the temperature side, when the switch 20 is changed to the side of the current control circuit 16, but the body heater 3 is easily heated by the set value in the current setting part 15.
On the other hand, for the tip heater 2, the conducting quantity which is previously set for preheating is determined by the preheat current setting part 18, the tip heater 2 is constantly heated through the changeover switch 20 with the current control circuit 8 and the power control circuit 5. The current value which is set in the tip current setting part 19 for switching a gate is changed by allowing to act the changeover switch 20 with the timer circuit 21 which acts in connection with the injection molding operation, thereby the temperature of the tip heater can be raised to a necessary setting temperature. Further, when the time of the timer circuit 21 is passed, the changeover switch 20 changes again to the opposite side, and the temperature of the tip heater 2 goes down to the preheat temperature.
Using the hot runner 1, which acts as described above, the heat insulation of molten resin in a runner part of an injection molding equipment, and the gate switch which is based on cooling hardening, heating and melting of the resin of a gate area adjacent to a cavity, can be smoothly conducted.
However, in the above conventional embodiment, since the temperature is generally controlled by an analog quantity and all of the indicators 4, 6, and 11 use the analog indication, there are many problems as follows.
(a) The controller including the body heater 3, the current control circuit 8 and 9 which control the tip heater 2, the power control circuits 5 and 7, the temperature control circuit 10 and the timer circuit 21 has many control parts for the analog control. Further, display and reading of the indicaters 4, 6 and 11 are inferior in accuracy.
(b) In the past, since one unit of an operation panel has been mounted on each hot runner 1, the more the number of the hot runner 1 has increased, the more the area occupied by the operation panel has increased. As the result, the whole controller construction inevitably has become a large size.
(c) In the past, an error has been easily made between the value which has been set by the length or the kind of the hot runner 1 and the actual current value. It has been caused by the complex control circuit based on the analog control. Further, the circuit has been expensive. It has been also difficult to obtain the desired accuracy owing to the change of temperature or voltage.
(d) The analog control has a problem in accuracy because there are individual differences in human operation such as adjustment or control.
(e) When remote control and group control are conducted, information of the temperature and current of each heater and system control and the like must be transferred. However, in the conventional analog system, it has been difficult to transfer the information.
(f) In the analog control, each control button of the temperature of the hot runner 1, the body current, the tip preheat and the tip current exists for each hot runner 1. As a result, the more the number of the hot runner is increased, the more the set button is proportionally increased.